Cell-based immunotherapies are in active development for treatment of cancer, and adoptive cell therapy (ACT) with ex vivo activated/expanded T-cells is one of the most promising treatments currently being tested in patients. In ACT, autologous tumor-reactive T-cells are activated/expanded ex vivo and then reinfused to combat metastatic tumors. However, strategies to protect T-cells from the highly immuno-suppressive environment generated by tumors are needed to increase the frequency and durability of objective responses. We recently demonstrated that the efficacy of ACT can be dramatically enhanced by conjugation of cytokine- loaded nanoparticles (NPs) to the surfaces of T-cells ex vivo prior to transfer into tumor-bearing recipients (Stephan et al. Nat. Med. 2010). T-cell-bound particles provided pseudo-autocrine drug delivery to the transferred cells that greatly increased the effective potency of adjuvant cytokines while simultaneously eliminating systemic exposure to the drug. However, a limitation of this approach is the one-time nature of the intervention: ACT T-cells can only be loaded once with a cargo of adjuvant drug prior to transfer, and the duration of stimulation is inherently limited by expansion of the cell population in vivo. What is needed is a strategy to arm T-cells with nanoparticle drug carriers in vivo, directly in th blood or tissues, so that a single population of anti-tumor lymphocytes transferred into a patient could be repeatedly stimulated with supporting adjuvant drugs that are targeted to this cell population. We propose a set of approaches to achieve this goal, based on the injection of nanoparticles that carry immunosuppression-blocking adjuvant drugs, which are designed to bind to tumor cells and/or ACT T-cells, and which could be re-administered at will to continuously provide supporting signals to lymphocytes during ACT therapy. As a proof of concept, we will focus on delivery of a small-molecule inhibitor of the key T-cell phosphatase Shp1, which is a downstream target of a broad spectrum of negative regulatory signals in the tumor microenvironment including IL-10, TGF-, CTLA-4, and PD-1. We propose to test 3 major strategies, which are not mutually exclusive: (i) non-specific in situ targeting of NPs to tumor cells and lymphocytes via thiol-reactive particles; (ii) antibody-targeted NP delivery of Shp inhibitors specifically to ACT T-cells; and (iii) combined costimulation and targeting of ACT T-cells, by targeting Shp inhibitor-carrying NPs to ACT T-cells via stimulatory ligands that both target NPs to the T-cells and provide an activating/costimulatory signal to the recipient cells. As a final goal we will test whether the most potent of these approaches can synergize with vaccination to allow endogenous T-cell responses to have anti-tumor efficacy, thereby eliminating the need for adoptive transfer of T-cells for potent tumor rejection.